Joining method and assembly for an aircraft

ABSTRACT

A joining method and assembly for an aircraft. To improve the characteristics or permit hitherto impossible connections between thermoplastic and thermoset components, a multi-material joining method is disclosed in which a thermoplastic connecting region is formed on the thermoplastic component. The connecting region is connected to the thermoset component by interdiffusion. For this purpose, the uncured second component is brought into contact with the connecting region and heat is supplied. An interdiffusion layer is formed which fixedly connects the second component and the connecting region to one another and thus joins the first component to the second component.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to German Patent Application Serial No.10 2020 109 740.9 filed Apr. 7, 2020, the entire disclosure of which isincorporated by reference herein.

TECHNICAL FIELD

The disclosure herein relates to a joining method for joining a,preferably fiber-reinforced, first component to a fiber-reinforcedsecond component. The disclosure herein also relates to an assembly foran aircraft.

BACKGROUND

Fiber-reinforced components are used in aviation on account of a widerange of advantages. In order to produce relatively large assemblies,use can be made of customary joining methods such as riveting, adhesivebonding, welding and interdiffusion joining. One example of film-basedinterdiffusion joining (film interdiffusion joining, FIDJ) is known fromEP 3 124 208 A1.

Some of the known methods can cause a high manufacturing outlay.Furthermore, not all of the methods are suitable for every type ofmaterial pairing. It may in particular be desirable for the connectionto be adapted to the desired function of the components to be connected,which is typically set by the geometry and the material properties ofthe components. This can be difficult in the case of adhesive bonds andwelded connections.

SUMMARY

The disclosure herein is based on an object of improving connectionsbetween fiber-reinforced components, preferably with regard to the loadproperties in the case of inhomogeneous loads.

The object is achieved by the subject matter disclosed herein.

The disclosure herein provides a joining method for joining a,preferably fiber-reinforced, first component, which contains a firstpolymer material as matrix, to a, preferably fiber-reinforced, secondcomponent, which contains a second polymer material as matrix, themethod comprising:

a) providing the first component;

b) forming a connecting region on the first component in order togenerate a joining surface on the first component, the connecting regioncomprising one or more thermoplastic polymer materials and being formedwith at least one of the following features:

ba) the connecting region is formed with a plurality of adjacent spatialregions, at least two adjacent spatial regions comprising differentthermoplastic polymer materials; and/or

bb) the connecting region is formed with a surface structure regionwhich has periodic elevations and indentations in at least onedirection;

c) arranging a region of the second component so as to be in contactwith the joining surface and supplying heat in order to fix theconnecting region to the second component, preferably with formation ofan interdiffusion layer in order to join the first component to thesecond component.

It is preferable that, in step ba), the connecting region is formed witha first spatial region and a second spatial region.

It is preferable that the first spatial region is composed of the firstpolymer material and the second spatial region is composed of athermoplastic polymer material which is different from the first polymermaterial.

It is preferable that the first spatial region contains short fibersand/or continuous fibers. It is preferable that the second spatialregion contains short fibers and/or continuous fibers.

It is preferable that the first spatial region and the second spatialregion are formed adjacently in a sheet-like layer of the connectingregion, the layer being parallel to the joining surface. It ispreferable that the first spatial region and the second spatial regionare formed adjacently in a thickness direction of the connecting region,the direction extending normal to the joining surface.

It is preferable that, in step ba), the connecting region is formed witha plurality of first and second spatial regions. It is preferable that,as viewed in a thickness direction which extends normal to the joiningsurface, the extent of the first spatial regions gradually decreaseswith increasing distance from the first component, whereas the extent ofthe second spatial regions gradually increases. It is preferable thatthe first and second spatial regions are arranged in alternation in thethickness direction. It is preferable that the first and second spatialregions form a cellular structure and/or wavelike structure. It ispreferable that the first and second spatial regions are formed, andarranged, in such a way that, in the thickness direction, there is agradual transition from the first polymer material to the polymermaterial or to the polymer materials that the connecting regioncontains.

It is preferable that the fibers in the first spatial region extendpredominantly in a first direction and the fibers in the second spatialregion extend predominantly in a second direction which is differentfrom, preferably orthogonal to, the first direction.

It is preferable that, in step ba), a spatial region is configured inthe form of a core region of the connecting region, the core regionbeing arranged in such a way that the core region encompasses merely thecomponents and adjacent spatial regions. Preferably, the first spatialregion and/or the second spatial region are/is a core region. It ispreferable that the core region is composed of a, preferablyfiber-reinforced, thermoplastic polymer material.

It is preferable that, in step ba), a spatial region is configured inthe form of an outer edge region of the connecting region, the outeredge region being arranged in such a way that the outer edge regionextends along a periphery of the connecting region and encompassesmerely the components and the core region. Preferably, the first spatialregion and/or the second spatial region are/is an outer edge region. Itis preferable that the outer edge region is composed of a, preferablynon-reinforced, thermoplastic polymer material. It is preferable thatthe outer edge region has a lower melting temperature than the materialof the core region.

It is preferable that, in step ba), a spatial region is configured inthe form of an intermediate region of the connecting region, theintermediate region being arranged between the outer edge region and thecore region. Preferably, the first spatial region and/or the secondspatial region are/is the intermediate region. It is preferable that theintermediate region is composed of a, preferably non-reinforced,thermoplastic polymer material. It is preferable that the polymermaterial is identical to the polymer material of the core region. It ispreferable that the polymer material is different from the polymermaterial of the outer edge region. It is preferable that the polymermaterial has a higher melting temperature than the material of the outeredge region.

It is preferable that, in step ba), the surface structure region isformed on a side of the connecting region, the side facing away from thejoining surface. It is preferable that, in step ba), in a plane parallelto the joining surface, the surface structure region is formed withelevations and indentations, which are preferably of wavelike design,and/or a corrugated or serrated pattern. It is preferable that, in stepba), the surface structure region is formed in such a way that, in aplane parallel to the joining surface, a form fit is formed between theconnecting region and the first component.

It is preferable that the first polymer material is a thermoplasticpolymer material or a thermosetting polymer material. It is preferablethat the second polymer material is a thermosetting polymer material. Itis preferable that the connecting region contains a polymer materialwhich preferably has a lower melting temperature than the first polymermaterial.

It is preferable that step a) and step ba) are effected by additivemanufacturing. It is preferable that step a) and step ba) are effectedby additive manufacturing in such a way that first the connecting regionis manufactured and subsequently the first component is manufactured.

The disclosure herein also provides an assembly, preferably for anaircraft, obtainable by implementation of a joining method as describedabove.

One idea is to join together components composed of composite materialswhich have different matrix systems. Typical components in the aviationsector are for instance clamps, clips, fastening eyes, stringers,formers, skins and the like. As in the case of the conventional methods,weight, certification, manufacturing outlay, manufacturingrepeatability, damage tolerance, load capacity and the like have to betaken into account. These aspects can be improved by the disclosureherein.

By way of example, “kissing bonds” can be avoided by way ofinterdiffusion bonds. In the disclosure herein, there is the additionalfactor that the conventional methods generate a homogeneous connection,for example by way of homogeneous material properties and geometries, atpoints which are generally subjected to inhomogeneous loading. Theelongation in the substrates can thus lead to local stress increases inthe edge regions or peel loads as a result of eccentric loading.

One proposal is to utilize the interdiffusion of multiple materials,which can be referred to as multi-material interdiffusion joining(M²IDJ). This type of connection can preferably be generated by additivemanufacturing by filament layer manufacturing (FLM). The connectionpermits an increased load capacity and damage tolerance. At the sametime, the structural weight and the manufacturing outlay can be reduced.

The use of multiple materials and the superior capabilities of 3Dprinting to realize virtually any desired geometries make it possible toadapt the structure of the connecting region and interdiffusion zones tothe expected load scenarios in advance. M²IDJ can, on the one hand, beimplemented on the conventional film geometry or for connecting3D-printed thermoplastic components to thermoset components.

For adaptation purposes, it is possible to vary, inter alia, thefollowing parameters:

-   -   thermoplastics with different solubility in the thermoset matrix    -   thermoplastics with different material strength and stiffness    -   thermoplastics with high/low fracture toughness    -   microadditives (particles) and macroadditives (fibers)    -   material connection zone architecture (material design, film        thickness, porosity, production route, reorientation of        additives)

Typically used thermoplastics are high-performance thermoplastics, forexample polyaryletherketones (PAEK), such as polyetheretherketone (PEEK)and polyetherketoneketone (PEKK). Examples of thermoplastics with arelatively low melting temperature are polyetherimides (PEI), blendscomposed of PEI and polycarbonate (PC), thermoplastic polyurethane(TPU), and also polyamides. Typical thermoset systems are epoxy resins,for example. The thermoplastics can preferably contain fill material,for example particles or fibers (both short fibers and continuousfibers).

The connection can be adapted to shearing, peeling, tearing, cleavageand the like in various manners. In the case of inhomogeneous joinloading, such as shearing, peeling, cleavage, the relevant module can beadapted. For stresses of this kind, it is thus possible for additives(for example fibers, particles) to be embedded in the thermoplastic inorder to increase, for example, the shear modulus in the direction ofthe expected loading. The fibers can in this case extend in differentpreferred directions. It is also conceivable to use a preferablystructured multi-matrix.

A further adaptation possibility is edge strengthening, in the case ofwhich, for example in an edge region of the connecting region, the fiberorientation is adapted, or merely the pure matrix or a tougher matrix isapplied.

A further measure may be to locally apply toughparticles/lines/patterns, with the aim of bridging cracks. Furthermore,it is possible to provide pores or poorly bonded fibers in order to pincracks. The pores can also function as crack arrestors. A further ideais for a tough matrix with bonding to the main matrix to be locallyprovided in order to deflect the crack path. A preferred refinement cancontain microparticles or other additives—for example rubber particlesor TPU—in order to distribute, and thus reduce, shear forces. Anotherrefinement can contain high-modulus additives, such as graphite, carbonnanotubes or carbon black, for prevention of microcracks.

A further idea is for highly tough local phases composed ofthermoplastic having a melting temperature below the infusiontemperature to be provided for the purpose of bonding to textile partsor preforms. Furthermore, a perforation can be provided in theconnecting region as an infusion aid.

For bonding of polymers of different types, a transition phase or atransition region can be formed in the connecting region. Ideally, thetransition has a gradual cellular geometry. Crossovers between differentmaterial phases are also possible. By way of example, it is possible toinitially print PEI as a connecting region, and subsequently PEEK forthe actual component. In this case, the two materials can be locallyfused on account of the relatively high melting temperature of PEEK.

A further idea is for the connecting region to be provided with asurface structure, by which the connecting region is connected to thecomponent, whereas the joining surface remains smooth. The surfacestructure can advantageously be generated by additive manufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be explained in more detail with reference tothe appended schematic drawings, in which:

FIG. 1 through FIG. 8 show example embodiments of an assembly;

FIG. 9 shows detail views (a) through (f) of different examples ofconnecting regions; and

FIG. 10 through FIG. 13 show an example embodiment of a joining method.

DETAILED DESCRIPTION

Reference is first of all made to FIG. 1 , which shows an assembly 10.The assembly 10 comprises a first component 12 and a second component14, which are connected to one another via a connecting region 16.

The assembly 10 is for example intended for an aircraft. The firstcomponent 12 can be a reinforcing component, for instance a stringer.The second component 14 can be a fuselage component, for example anouter skin which is intended to be reinforced by the first component 12.

The first component 12 is a fiber-reinforced component which contains amatrix composed of a first polymer material 18. The first polymermaterial 18 is selected from the group of polyaryletherketones, forexample PEEK.

The second component 14 is a fiber-reinforced component which contains amatrix composed of a thermosetting second polymer material 20. Thesecond polymer material 20 is for example epoxy resin.

The connecting region 16 is composed of a thermoplastic polymermaterial, for example PEI. The connecting region 16 can be configured inthe form of a film or in the form of a foil.

The first component 12 and the connecting region 16 are fused togetherat a melt layer 22. This can be achieved for example in that the firstcomponent 12 is additively manufactured on the connecting region 16.

The connecting region 16 also has a joining surface 24 which preferablylies opposite the melt layer 22.

The second component 14 is arranged with a region in contact with thejoining surface 24. In this state, the second polymer material 20 isstill in the curable state. Heat is then supplied in order to heat thefirst polymer material 18 above its glass transition temperature and toactivate the curing of the second polymer material 20. In this case, aninterdiffusion layer 26 is produced between the second component 14 andthe connecting region 16. The connecting region 16 is then fixed to thesecond component 14, and therefore overall the first component 12 andthe second component 14 have been joined to form the assembly 10.

The further example embodiments are explained merely insofar as theydiffer from the example described above.

As indicated in FIG. 2 , the connecting region 16, similarly to thefirst component 12, is generated by additive manufacturing. In thesequence, the connecting region 16 is initially generated and then thefirst component 12 is constructed on the connecting region 16. Themethod then proceeds as described above.

FIG. 3 shows a connecting region 16 which is additively manufacturedfrom a fiber-reinforced thermoplastic first polymer material 18, forexample fiber-reinforced PEI. The fibers are for example continuousfibers and can be arranged at angles of +45° and −45°.

It is also possible for the connecting region 16 to contain more thanone layer, with a fiber direction that alternates in each case fromlayer to layer. Accordingly, the connecting region 16 has a firstspatial region 28 with a first fiber direction and a second spatialregion 30 with a second fiber direction, which may be orthogonal to thefirst fiber direction. The method then proceeds as described above.

It should be noted that the second spatial region 30 is considered to becomposed of a different polymer material compared with the first spatialregion 28 because the fibers extend in another direction.

FIG. 4 shows a connecting region 16 which is additively manufactured.The connecting region 16 contains a first spatial region 28 and a secondspatial region 30.

The first spatial region 28 is configured in the form of an outer edgeregion 32. The outer edge region 32 has an exposed side 33. The outeredge region 32 is for example composed of non-reinforced thermoplastic,such as PEI.

The second spatial region 30 is configured in the form of a core region34. The core region 34 adjoins the outer edge region 32, the firstcomponent 12 and the second component 14. The core region 34 is forexample composed of fiber-reinforced thermoplastic, such as PEI. Thecore region 34 can have different fiber directions, as described above.

FIG. 5 shows a connecting region 16 which is additively manufactured.The connecting region 16 contains a first spatial region 28 and a secondspatial region 30.

The first spatial region 28 is configured in the form of an outer edgeregion 32 and in the form of a core region 34. The first spatial region28 is for example composed of a fiber-reinforced thermoplastic such asPEI, wherein the fibers extend at an angle of 90° relative to the firstcomponent 12 or the second component 14.

The second spatial region 30 is configured in the form of anintermediate region 36 which is arranged between the outer edge region32 and the core region 34. The second spatial region 30 is for examplecomposed of a fiber-reinforced thermoplastic such as PEI.

In contrast to the first spatial region 28, the fibers extend at anangle of 0°. It should be noted that the second spatial region 30 isconsidered to be composed of a different polymer material compared withthe first spatial region 28 because the fibers extend in anotherdirection.

FIG. 6 shows a connecting region 16 which is additively manufactured.The connecting region 16 contains a first spatial region 28, a secondspatial region 30, a third spatial region 38 and a fourth spatial region40.

The first spatial region 28 is configured in the form of an outer edgeregion 32. The outer edge region 32 is composed of a non-reinforcedthermoplastic polymer material, for example polyamide or thermoplasticpolyurethane, wherein the polymer material has a low meltingtemperature.

The second spatial region 30 is configured in the form of anintermediate region 36. The intermediate region 36 is composed of anon-reinforced thermoplastic polymer material such as PEI. Theintermediate region 36 has a higher melting temperature than the outeredge region 32.

The third spatial region 38 is configured in the form of a furtherintermediate region 42 which is arranged between the intermediate region36 and the core region 34. The further intermediate region 42 iscomposed of a fiber-reinforced thermoplastic polymer material such asPEI, in which the fibers extend at an angle of 90°.

The fourth spatial region 40 is configured in the form of a core region34. The core region 34 is composed of a fiber-reinforced thermoplasticpolymer material such as PEI, in which the fibers extend at an angle of0°.

FIG. 7 shows a connecting region 16 which is additively manufactured.The connecting region 16 is formed with a surface structure region 44 onwhich the melt layer 22 is formed. The surface structure region 44 isstructured such that a form fit is generated in a plane parallel to thejoining surface 24. The surface structure region 44 can haveperiodically alternating elevations 46 and indentations 48. The surfacestructure region 44 can be configured in a wavelike manner, with agrooved or serrated pattern and/or the like.

FIG. 8 shows a connecting region 16 which is additively manufactured.The connecting region 16 is formed such that, in the thickness directionD, there is a gradual transition between the polymer material of theconnecting region 16 and the first polymer material 18. By way ofexample, a plurality of polymer layers 50 are generated, wherein theproportion of polymer lines composed of the first polymer material 18increases layer by layer. The first spatial region 28 and the secondspatial region 30 are produced by the various polymer lines.

FIG. 9 shows further examples of such a system composed of polymerlayers 50 with the first spatial region 28 and the second spatial region30. The transition can be designed in the form of a cellular structureor regions which are arranged periodically in alternation, as areillustrated in FIG. 9 .

The joining method is elucidated with reference to FIG. 10 to FIG. 12 .The first component 12 is initially provided with the connecting region16. The provision can be effected in that the first component 12 and theconnecting region 16 are additively manufactured. Preferably, theconnecting region 16 is manufactured first or at the same time as thefirst component 12. The connecting region 16 is configured in any, or anexpedient, combination of the examples described above.

Looking at FIG. 11 , a region of the second component 14 is brought intocontact in the uncured state with the joining surface 24. The secondcomponent 14 can be a textile preform, a carbon fiber-reinforcedplastics part or the like. If required, the second component 14 isinfused in the position.

As illustrated in FIG. 12 , the assembly 10 is subsequently finished bysupply of heat. The first component 12 is then joined to the secondcomponent 14 to form the assembly 10, which is schematically illustratedin FIG. 13 .

In order to improve the characteristics or permit hitherto impossibleconnections between thermoplastic and thermoset components 12, 14, amulti-material joining method is proposed in which a thermoplasticconnecting region 16 is formed on the thermoplastic component 12. Theconnecting region 16 is connected to the thermoset component 14 byinterdiffusion. For this purpose, the uncured second component 14 isbrought into contact with the connecting region 16 and heat is supplied.An interdiffusion layer 26 is formed which fixedly connects the secondcomponent 14 and the connecting region 16 to one another and thus joinsthe first component 12 to the second component 14.

While at least one example embodiment of the present invention(s) isdisclosed herein, it should be understood that modifications,substitutions and alternatives may be apparent to one of ordinary skillin the art and can be made without departing from the scope of thisdisclosure. This disclosure is intended to cover any adaptations orvariations of the example embodiment(s). In addition, in thisdisclosure, the terms “comprise” or “comprising” do not exclude otherelements or steps, the terms “a”, “an” or “one” do not exclude a pluralnumber, and the term “or” means either or both. Furthermore,characteristics or steps which have been described may also be used incombination with other characteristics or steps and in any order unlessthe disclosure or context suggests otherwise. This disclosure herebyincorporates by reference the complete disclosure of any patent orapplication from which it claims benefit or priority.

LIST OF REFERENCE DESIGNATIONS

-   -   10 Assembly    -   12 First component    -   14 Second component    -   16 Connecting region    -   18 First polymer material    -   20 Second polymer material    -   22 Melt layer    -   24 Joining surface    -   26 Interdiffusion layer    -   28 First spatial region    -   30 Second spatial region    -   32 Outer edge region    -   33 Exposed side    -   34 Core region    -   36 Intermediate region    -   38 Third spatial region    -   40 Fourth spatial region    -   42 Further intermediate region    -   44 Surface structure region    -   46 Elevation    -   48 Indentation    -   50 Polymer layer    -   D Thickness direction

The invention claimed is:
 1. A joining method for joining togetherfiber-reinforced first and second components, the method comprising:forming a connecting region, which comprises one or more thermoplasticpolymer materials and is formed with a surface structure region;forming, via additive manufacturing, a first fiber-reinforced component,which comprises a first polymer material as matrix, on the connectingregion, such that the connecting region and the first component areattached together to provide a joining surface on the first component;forming a second fiber-reinforced component, which comprises a curablethermosetting second polymer material as matrix; and arranging, afterthe connecting region and the first component are attached together, aregion of the second component in contact with the joining surface andsupplying heat to fix the connecting region to the second componentwhile curing the second polymer material to join the first component tothe second component; wherein the surface structure region comprisesperiodic elevations and indentations in at least one direction and isformed on a side of the connecting region that faces away from thejoining surface; and wherein, in a plane parallel to the joiningsurface, the elevations and the indentations are of wavelike designand/or a corrugated or serrated pattern.